1. Field of the Invention
This invention relates generally to fuel filters employed in connection with internal combustion engines. More particularly, the present invention relates to a base receptacle which receives a replaceable fuel filter cartridge to form a filter assembly for removing foreign particles and/or separating water from the fuel supply system of an internal combustion engine.
2. Description of the Related Art
Fuel filter systems to which the invention relates commonly employ a disposable filter cartridge that is replaced at pre-established intervals of filter usage. The replaceable cartridge is conventionally secured to a base that defines inlet and outlet connections between the cartridge and the fuel supply system. Numerous retention systems have been employed for securing the filter cartridge to the base and allowing removal of the cartridge for replacement purposes.
Filter assemblies to which the present invention relates are typically mounted to motor vehicles such as automobiles, trucks, farm equipment, industrial equipment and construction equipment such as bulldozers. Operation of these types of equipment frequently exposes the filter assembly to extreme vibration and shock. To be commercially viable, a filter system must reliably maintain a sealed relationship between the disposable filter cartridge and the base. Filter cartridge replacement should be simple and preferably accomplished without tools.
The disposable filter cartridge is conventionally secured to the filter assembly base by a retaining or locking mechanism, which is releasable to allow for the removal of the cartridge for replacement purposes. There are numerous conventional fuel filter cartridge base retention systems. In U.S. Pat. No. 5,017,285, which is assigned to the assignee of the present invention, one disclosed inverted fuel filter assembly employs a base that mounts to the vehicle and a disposable filter cartridge that is suspended directly below the base. The cartridge is retained to the base by a threaded collar. The collar includes a shoulder that retentively engages against a roll seam structure at the periphery of the cartridge housing. The collar threads to the base. The cartridge is replaced by loosening the threaded collar and dismounting the filter cartridge. While this type of retainer device performs in an acceptable manner, the threaded collar can introduce uneven loading between different fuel filter assemblies as well as within a given fuel filter depending upon the degree of tightening or torque applied to the retainer collar. In addition, the threads are subject to exposure to various fluids and particulate matter, which may seriously jeopardize the integrity and efficiency of the threaded engagement. In the field, it is often problematical to ascertain the proper torque or tightening technique that should be applied to properly secure the cartridge to the base.
U.S. Pat. Nos. 5,203,994 and 5,302,284, both assigned to the assignee of the present invention (hereinafter the '994 and '284 patents, respectively) exemplify improvements to the basic filter system disclosed in the '285 patent discussed above. The '994 and '284 patents describe a filter system in which the threaded attachment is replaced by a spiral ramp structure on the base and a complementary follower structure in the retainer collar. The base includes a stop angularly spaced from an upper end of the spiral ramp structure of the base. The follower structure includes a catch configured to seat between the upper end of the base spiral ramp and the angularly spaced stop. The '994 patent discloses a spring disposed between the received end of the cartridge and the base to releasably maintain the locked position of the collar follower over the upper end of the base spiral ramp by biasing the cartridge and collar away from the base. The '284 patent discloses a collar that carries a wave spring to bias the collar away from the base and maintain the locked position of the collar follower over the upper end of the base spiral ramp. Each of the spring members is configured to evenly distribute the load between the base and the cartridge.
An alternative filter cartridge mounting system is disclosed in U.S. Pat. No. 6,187,188, also assigned to the assignee of the present invention. The roll seam at the junction of the cartridge housing sections is radially outwardly displaced to form a plurality of retention tabs. The base includes a fixed retaining structure comprising a retaining lip defining a plurality of axial slots in communication with retaining channel portions above the retaining lip. An upper surface of the retaining lip defines a ramp leading to a seat axially below the top of the ramp. The filter cartridge is retained to the base by axially aligning the tabs with the slots and upwardly displacing the cartridge into the receptacle of the base. The cartridge is then rotated so that the tabs ride up the ramps and into the seats. A resilient radial extension of the central sealing grommet provides a biasing force between the received end of the filter cartridge and the base. This biasing force maintains the tabs in their seats and resists unintentional reverse rotation of the cartridge relative to the base.
While the above-discussed filter cartridge retention systems perform in an acceptable manner and have proven commercially successful, further enhancements in the security of cartridge retention that do not complicate filter assembly construction or cartridge replacement may be possible.